On May 10, 9:14 pm, "David B. Benson" <[EMAIL PROTECTED]> wrote:
> On May 9, 3:29 pm, Alastair <[EMAIL PROTECTED]> wrote:
>
> >...
> > I understand the difference but find it
> > difficult to explain it.
>
> Please give it a try. :-)
If the earth's orbit around the sun was a perfect cirle, then the
solar flux reaching earth would be the same throughout the year, and
the caloric equaror would be the same as the geographical equator.
The earth's orbit is an ellipse with the sun at one focus, and so
during the year at times the earth is closer to the sun (perihelion)
and further from the sun (aphelion.) If perihelion occurs during the
southern hemisphere's summer then the caloric equator is moved into
the southren hemisphere. If perihelion occurs during the northern
hemiisphere's summer (southern hemisphere's winter) thenthe caloric
equator moves into the northern hemisphere. Perihelion does move
between the two hemispheres with a 22 ka cycle. It is one of the
Milankovitch cycles See
http://en.wikipedia.org/wiki/Milankovitch_cycles#Precession_.28wobble.29
The ITCZ is a meteorlogical feature which is a cloud belt around the
tropics. It moves on an annual cycle (following the sun) but does not
follow a line of latitude since it is modified by the presence of land
and sea. It tends to move further poleward over land, and since there
is more land in the northern hemisphere on average it is in the
northern hemisphere. (At present the caloric equator is in the
southern hemisphre because perihelion happen in January.)
The extreme seasonal positions of the ITCZ are shown here.
http://en.wikipedia.org/wiki/ITCZ Note that in the Amazon the ITCZ
remains roughly in the same position during the year. If the caloric
equator moves then it is likely that the position of the ITCZ in
Amazonia will also move.
However, when the perihelion occurs during the SH summer, snow is more
likely to remain unmelted in the NH summer, resulting in NH
glaciation. With the NH land covered in ice the ICTZ, will move south
on average. So when the caloric equator is in the SH, then the ITCZ is
likely to be further south than 'usual'.
HTH,
Cheers, Alastair.
. the caloric equator is set by the position of the sun in the sky.
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